In recent years, in a cellular mobile communication system, with the development of information multimedia, it is common to transmit a large quantity of data, such as still image data and motion image data, as well as sound data. In order to realize transmission of a large quantity of data, studies have been actively performed as to a technique for realizing a high transmission rate using a high-frequency radio band.
However, when a high-frequency radio band is used, a high transmission rate can be achieved over a short distance, but attenuation increases depending on the transmission distance over a longer distance. Accordingly, when a mobile communication system is actually operated using a high-frequency radio band, the cover area of a wireless communication base station apparatus (hereinafter, simply referred to as a base station) decreases, requiring more base stations. More base stations are provided with commensurate cost, thus there is a demand for a technique which suppresses an increase in the number of base stations and realizes a communication service using a high-frequency radio band.
With regard to the above-described demand, a relay transmission technique has been studied: a wireless communication repeater station apparatus (hereinafter, simply referred to as a repeater) is provided between a base station and a wireless communication mobile station apparatus (hereinafter, simply referred to as a mobile station) so as to expand the cover area of the base station. Thus, communication is performed between the base station and the mobile station through the repeater. If the relay transmission technique is used, even a terminal which cannot perform direct communication with the base station can perform communication through the repeater. The mobile station may have the function of the repeater.
In the related art, in order to obtain the reception diversity effect at the base station (eNB), cooperative relay (coded cooperation) has been suggested in which a plurality of terminals (hereinafter, referred to as repeater) having a repeater function participate. Cooperative relay may be called collaborative relay or corporate relay.
FIG. 23 is a schematic view of a cooperative relay system which carries out cooperative relay between repeaters 1001 and 1002 and a base station 1003. FIG. 24 shows an operation example of the cooperative relay system of FIG. 23.
An operation example of cooperative relay which is realized by the cooperative relay system of FIG. 23 will be described focusing on the operation of the repeater 1001 of FIG. 24.
Procedure 1-1: The repeater 1001 segments transmission data to be transmitted to the base station (eNB) into two pieces of data of initial transmission data S1 including a systematic bit and parity data P1.
Procedure 1-2: The repeater 1001 transmits initial transmission data S1 to the repeater 1002 and receives initial transmission data S2 from the repeater 1002 (see FIG. 23(a)).
Procedure 1-3: The repeater 1001 generates parity data P2 from received initial transmission data S2.
Procedure 1-4: Thereafter, the repeater 1001 transmits initial transmission data S1 at the local station to the base station (eNB) 1003 (see FIG. 23(b)) and subsequently transmits generated parity data P2 to the base station (eNB) 1003 (FIG. 23(c)).
Similarly, the operation of the repeater 1002 of FIG. 24 will be described.
Procedure 2-1: The repeater 1002 segments transmission data to be transmitted to the base station (eNB) into two pieces of data of initial transmission data S2 including a systematic bit and parity data P2.
Procedure 2-2: The repeater 1002 transmits initial transmission data S2 to the repeater 1001 and receives initial transmission data S1 from the repeater 1001 (see FIG. 23(a)).
Procedure 2-3: The repeater 1002 generates parity data P1 from received initial transmission data S1.
Procedure 2-4: The repeater 1002 transmits initial transmission data S2 at the local station to the base station (eNB) 1003 (see FIG. 23(b)) and subsequently transmits generated parity data P1 to the base station (eNB) 1003 (FIG. 23(c)).
The timing of initial transmission of data at each repeater is called a first-frame, and the timing of transmission of parity data at the other station is called a second-frame.
With the above, the base station (eNB) 1003 receives two pieces of segmented data of the repeaters 1001 and 1002 through different paths (that is, cooperative relay), obtaining the path diversity effect.
As described above, when there is no significant difference in reception quality at the time of reception at the base station (eNB), cooperative relay is successful, obtaining the path diversity effect.
However, there may be a significant difference in the propagation environment (propagation quality) between the base station (eNB) 1003 and the repeater 1001 and between the base station (eNB) 1003 and the repeater 1002. In this case, a significant difference in reception quality may occur in received data of the repeaters at the base station (eNB) 1003, and as a result, the path diversity effect may not be obtained.
FIG. 25 is a schematic view of the cooperative relay system when there is a difference in the propagation environment (propagation quality) between the base station (eNB) 2003 and each of the repeaters 2001 and 2002. FIG. 26 shows an operation example of the cooperative relay system of FIG. 25.
In the cooperative relay system of FIG. 25, it is assumed that the propagation environment (propagation quality) between the base station (eNB) 2003 and the repeater 2002 is poor.
An operation example of cooperative relay which is realized by the cooperative relay system of FIG. 26 will be described focusing on the operation of the repeater 2001 of FIG. 25.
Procedure 1-1: The repeater 2001 segments transmission data to be transmitted to the base station (eNB) into two pieces of data of initial transmission data S1 including a systematic bit and parity data P1.
Procedure 1-2: The repeater 2001 transmits initial transmission data S1 to the repeater 2002 and receives initial transmission data S2 from the repeater 2002 (see FIG. 25(a))
Procedure 1-3: The repeater 2001 generates parity data P2 from received initial transmission data S2.
Procedure 1-4: Thereafter, the repeater 2001 transmits initial transmission data S1 at the local station to the base station (eNB) 2003 (see FIG. 25(b)) and subsequently transmits generated parity data P2 to the base station (eNB) 2003 (FIG. 25(c)).
Similarly, the operation of the repeater 2002 of FIG. 25 will be described.
Procedure 2-1: The repeater 2002 segments transmission data to be transmitted to the base station (eNB) 2003 into two pieces of data of initial transmission data S2 including a systematic bit and parity data P2.
Procedure 2-2: The repeater 2002 transmits initial transmission data S2 to the repeater 2001 and receives initial transmission data S1 from the repeater 2001 (see FIG. 23(a)).
Procedure 2-3: The repeater 2002 generates parity data P1 from received initial transmission data S1.
Procedure 2-4: The repeater 2002 transmits initial transmission data S2 at the local station to the base station (eNB) 2003. However, since the propagation environment (propagation quality) between the base station (eNB) 2003 and the repeater 2002 is poor, the reception quality of initial transmission data S2 at the base station (eNB) 2003 is degraded and in the worst case, initial transmission data S2 may not be received (see FIG. 25(b)). Similarly, the repeater 2002 transmits generated parity data P1 to the base station (eNB). However, since the propagation environment (propagation quality) between the base station (eNB) 2003 and the repeater 2002 is poor, the reception quality of parity data P1 at the base station (eNB) 2003 is degraded and in the worst case, parity data P1 may not be received (FIG. 25(c)).
As described above, when there is a significant difference in the propagation environment (propagation quality) between the base station (eNB) 2003 and the repeater 2001 and between the base station (eNB) 2003 and the repeater 2002, a significant difference in reception quality may occur in received data of the repeaters at the base station (eNB) and as a result, the path diversity effect may not be obtained.